1. Field of the Invention
The present invention is directed to an initially liquid coating which adheres to a substrate and cures to form a solid coating thereon. In particular, the present invention is directed to an intumescent coating which has heat resistant and fire retardant qualities and is somewhat impact resistant upon curing.
2. Prior Art
It is either desirable or required to provide heat insulating and flame retardant characteristics to certain substrates. For example, piping or pipelines in a variety of applications, such as petrochemical processing plants, have a history of fire related accidents so that a heat resistant and fire retardant coating is advantageous on various pipes and pipelines. The piping may be composed of metal, however, various polymeric pipes are also used. In addition, various types of pipes are repaired with a carbon fiber reinforced polymeric composite system. The repaired pipe which is covered and coated with a polymeric composite system is susceptible to extreme heat and fire and will burn or melt. In the event the pipe is breached, additional flammable fluids may be released. Accordingly, a fire retardant coating would be desirable.
Various coatings and compositions have been developed over the years which can provide heat resistance and fire retardant characteristics to substrates. In general, known intumescent coatings form a billowy, charred layer of material in the presence of a flame, thus, insulating the substrate from heat and flame.
Many existing fire retardant materials are either fibrous or ceramic based and, thus, are very brittle and easily damaged upon any impact. A ceramic based fire retardant system, known as Emisshield I-A™ licensed by Wessex, Inc. was evaluated along with the present invention. The Emisshield™ product sold for several hundred dollars per gallon, was extremely costly and had little impact resistance.
In addition, there are various known compositions including heat expandable graphite flakes which are known to provide flame resistance. The graphite flakes are treated with reagent chemicals which, upon exposure to heat, decompose and release gases. This forces apart the layers of the graphite planes and creates bubbling or expansion.
At the same time, in particular applications, the intumescent coating should be impact resistant. For example, at petrochemical processing plants there is considerable activity and, if the coating becomes brittle, it can fall off of the substrate upon slight impact.
In the past, there have been various attempts to provide fire retardant and similar compositions.
Schinabeck (U.S. Pat. No. 3,992,358) discloses a composition including glycidyl polyethers or epoxy resins having a hardening agent with inert fillers including graphite and fumed silica. The additional graphite fillers do not intumesce, and would not serve as a fire retardant. Moreover, Schinabeck does not contemplate expandable graphite flakes.
Yap (U.S. Pat. No. 5,389,435) discloses a flame retardant composition of epoxy derived from bisphenol-A with graphite fibers added as strength additives. The flame retardant mechanism is a light weight glass scim containing an inorganic filler and epoxy resin laminated to the composite.
Smith (U.S. Pat. No. 3,852,240) discloses an epoxy resin of the glycidyl ether type and an aliphatic or aromatic primary amine-containing compound without intumescent or fire retardant properties.
Liu (U.S. Pat. No. 6,084,008) discloses a fire retardant intumescent coating having a polymeric binder and expandable graphite particles which form individual units of self-expansion. Liu includes 25% to about 50% solvent, and does not include epoxy resins. Additionally, there is no suggestion of using fumed silica to improve the strength of the charred formulation.
Muraoka et al. (U.S. Pat. No. 6,472,070) discloses a fire retardant paint containing an epoxy resin and expandable graphite inorganic filler. Muraoka et al. does not suggest any use of fumed silica to provide impact resistance or to improve the strength of the charred formation.
Nakacho et al. (U.S. Pat. No. 6,528,559) discloses a flame retardant including phenoxy-phosphazene resin with inorganic filler such as silica.
Nevertheless, there remains a need to provide an intumescent coating that is heat and flame resistant and has impact resistance.
Accordingly, it is a principal object and purpose of the present invention to provide an intumescent coating for substrates which will expand upon reaction to heat or fire to provide heat resistant and fire retardant characteristics.
It is a further object and purpose of the present invention to provide an intumescent coating for a substrate which is waterproof and has impact resistance.